Apparatus for detecting objects

ABSTRACT

In apparatus for detecting an object by scanning two parallel paths having means for producing signals from radiation sensed by the scanning, an improvement comprises means for inhibiting the signal producing means at the limits of the scans. The inhibiting means comprise a shutter mounted for movement in synchronism with the scanning.

United States Patent McLeman 51 May 23, 1972 [54] APPARATUS FORDETECTING OBJECTS [56] References Cited [72] Inventor: Alexander D.McLeman, Corby, England UNITED STATES PATENTS 1 Assignee= g SteelCorporation, London, 3,541,337 1 1/1970 Brandenburg ..2s0/219 WD 22 i M25 1970 Primary Examiner-James W. Lawrence Assistant Examiner-D. C.Nelms [2l Appl. No.. 40,195 Anorney--Brady, OBoyle & Gates [30] ForeignApplication Priority Data [5 7] ABSTRACT v June 2, 1969 Great Britain..27,900/69 In apparatus for detecting an object by scanning twoparallel paths having means for producing signals from radiation [52]US. Cl. ..250/237 R, 250/219 LG, 250/219 WD, sensed by the scanning, animprovement comprises means for 0/ inhibiting the signal producing meansat the limits of the scans. Int. Cl. 'rhe means comprise a Shuttermounted for move- 0f l 1; 1 9 WD, LG, ment in synchronism the canning 5163 3Claims,7DrawingFigures AMPLIFIER F 'w E 6 73 1.0011: UNIT OUTPUTPULSE 77 7 AMPLIFIER 74 SHAPER 5 (ll) 71 \\(l//\) PATENTEDMAY 23 I972 3,665 2 O2 sum 1 OF 7 AMPLIFIER PULSE SHAPER 1 W .75

FIG. 1.

UNIT OUTPUT 77 7 (AMPLIFIER 74 s S/ SF ER 7U 72 f: mvsnron ALEXANDER D.McLEMAN BY @5 4 /z;

ATTORNEYS PATENTED MAY 2 3 I972 SHEET 3 BF 7 APPARATUS FOR DETECTINGOBJECTS The present invention relates to apparatus for detecting anobject.

Detection of objects is sometimes required for tracking and length orspeed measuring systems, for example in a steel bar rolling mill fordetecting bars leaving a mill.

In co-pending Patent Application Ser. No. 838,301, to Robert A. Senior,et al., filed 1st July 1969, and owned by the assignee of the presentapplication, there is disclosed apparatus for detecting an object whichcomprises a scanning arrangement for scanning two parallel paths and aradiation responsive arrangement co-operating with the scanningarrangement and comprising a pair of photo-diodes arranged to receivescanned radiation through respective apertures.

With this prior apparatus, the lengths of the scans are limited by theedges of the apertures. However, since the lens is arranged to focusonto the photo-diodes images of points where the objects to be detectedmay be present the edges of the apertures will appear out of focus tothe photo-diodes, and it is impossible to achieve a sharply definedcut-off simultaneously on the two scans.

It is an object of the present invention to provide an improvedapparatus for detecting an object by means of two scans wherein meansare provided for sharply and simultaneously cutting off both scans atthe ends thereof.

According to the present invention, means are provided for I inhibitingthe radiation responsive means at and adjacent the limits of the scans.

Further objects, features and advantages of the invention will appearfrom the following description of the apparatus illustrated in theaccompanying drawings, in which:

FIG. 1 shows diagrammatically an apparatus according to the aforesaidPatent Application Ser. .No. 838,301 for detecting an object;

FIG. 2 is a graphic representation of signals produced by the apparatusof FIG. 1; I r

FIG. 3 shows diagrammatically the apparatus of the present invention;

FIG. 4 is a schematic block diagram of the electrical circuit for theapparatus of FIG. 3;

FIG. 5 is an electrical schematic diagram of one of the amplifiercircuits designated in FIG. 4;

FIG. 6 is an electrical schematic diagram of the choppers amplifier ofFIG. 4; and

FIG. 7 is a schematic diagram of the logic unit of FIG. 4.

Referring to FIG. 1, a lens 1 is used to focus an image of two smallareas 4 and 5 of a roller table 16 (indicated in dotted lines) throughtwo apertures 2 and 3 respectively. Behind these aperture are twophoto-electric devices 17 and 18 respectively whose electrical responseis proportional to the amount of radiation coming through the apertures;i.e. to the radiation from the two small areas of the roller table underexamination. Photo-electric devices 17 and 18 are connected respectivelyto amplifiers 6 and 7 and the outputs of the two amplifiers 6 and 7 arepassed respectively to pulse shapers l3, l4 and thence to a logic unit15. The photo-electric devices 17 and 18 are conveniently photo-diodeseach connected in the biasing circuit of the associated amplifier 6 or7. The amplifiers 6 and 7 are conventional A C pulse amplifiers designedto supply an output voltage when the resistance of the associatedphoto-diode 17 or 18 falls sufiiciently i.e. when a sufficient quantityof radiation impinges on the photo-diode. The two small areas of theroller table exposed to the photo-diodes 17, 18 are constantly changedalong paths and 11 respectively transversely of the roller table byscanning means in the form of a rotating four-sided mirror 8 whichreflects the images onto a fixed mirror 9 which in turn reflects theimages to the lens 1. The paths l0 and 11 may overlap each otherslightly.

If a red hot bar 12 is in position (i) relative to the pathsscanned-there is sufficient radiation directed from the bar 12 to thephoto-diode 18 to produce an output signal from the amplifier 7 whilethere is insufficient radiation directed to the photo-diode 17 toproduce an output signal from the amplifier 6. As radiation from the bar12 impinges intermittently on the photo-diode 18 due to the rotation ofthe mirror 8, the output signal from the amplifier 7 is a series ofpulses.

If a bar 12 is in position (ii) relative to the scanned paths l0 and 11both amplifiers 6 and 7 will produce an output signal. Similarly with abar in position (iii) only the amplifier 6 will produce an outputsignal.

The unit 15, using conventional electronic logic techniques, can detectwhich ever of the three above conditions (i, ii, or iii of FIG. 1) isdesired.

For example if it is desired to detect the front end of a bar,(condition i,) the output of the logic unit would be as shown in FIG. 2.It should be noted that in this case the device would ignore any bars inpositions (ii) or (iii) of FIG. 1, i.e. the device would detect thefront of a bar even if the other bars are lying in the path scanned. At(i) (ii) and (iii) in FIG. 2 are shown the signals by the amplifiers 6,7 the pulse shapers 13, 14 and the logic unit 15 in response to objectsat positions (i), (ii) and (iii) respectively of FIG. 1.

The pulse shapers l3 and 14 and the logic unit 15 may conveniently becombined in a logic circuit comprising MEL Series 1O circuit blocksarranged (for condition 1) to produce an output only if the amplifier 7is at logic l and the amplifier 6 is at logic 0. The logic circuit isprovided with a delay circuit delaying for 40 1.4. sec the outputsignal, so that in the event of the photo-diode 18 being less sensitivethan the photo-diode 17 and hence the leading edge of the output pulsesof the amplifier 7 lagging the leading edge of the output pulses of theamplifier 6, a false detection is prevented.

With the above-described apparatus, the lengths of the scans are limitedby edges of the apertures 2 and 3. However, this arrangement has thedisadvantage that the limits of the scans maynot 72 be sufficientlyprecise for some applications since the lens 1 is arranged to focus onthe photo-diodes 17 and 18 images of points where the bars 12 to bedetected may be present and any other objects (e.g. the edges of theapertures 2 and 3) between said points and the lens will appear out offocus to the photo-diodes. Thus, the edges of the apertures 2 and 3appear out of focus and it is impossible to achieve a sharply definedcut-off simultaneously on the two scans. The scans may therefore beunequal in length and consequently an object (e.g. a hot bar) to bedetected lying adjacent a scan extremity may be detected by only one ofthe photo-diodes instead of two. The logic unit 15 is then presentedwith false information and will give an incorrect output.

The apparatus according to the present invention, shown in FIGS. 3through 7, in which parts which correspond to those in FIG. 1 have beenindicated by the corresponding reference numerals in the series, hasbeen designed to avoid such inaccuracy. In this apparatus, the rotatingmirror 108 is driven by a motor 119 through a drive belt 120 and aspindle 121 on which the mirror is mounted. Also mounted on the spindle121 is a chopper disc 122 having four vanes equally spaced apart roundits periphery. A Ga As cell 123 serving as a source of infra-redradiation and a photo-diode 124 serving as an infra-red detector arearranged on opposite sides of the disc 122 in positions such that thevanes on the disc intermittently prevent radiation from the cell 123from falling on the photodiode 124. The photo-diode 124 gives an outputonly when no vane is present between it and the cell 123. The outputfrom the photo-diode is amplified,and by an amplifier 126 (FIG. 4)applied to a logic unit 127 to inhibit the output from the logic unit127. The disc 122 is located on the spindle 121 so that each vanecorresponds with a side of the mirror 108. The leading edge of each vanedetermines when the output from the logic unit 127 ceases to beinhibited, and thus the effective starting point of each scan, andtherefore must be accurately set relative to the corresponding side ofthe mirror 108. The vane width determines the time that the logic unitoutput is not inhibited, and therefore the effective length of the scan.The logic unit 127 will give an output signal only if the followingconditions are satisfied:

a. Amplifier 106 output at logic 1 (i.e. billet detected) b. Amplifier107 output at logic (i.e. no billet detected) 0. The chopper amplifier126 at logic l If a billet were in such a position that it was detectedby both of the photo-diodes 117 and l 18, there is a possibility thatthe amplifier 106 would produce an output before the amplifier 107, dueto the variation in the sensitivities of the photodiodes 117 and 118. Ifthe leading edges of the output pulses of the amplifier 106 did notcoincide with those of the amplifier 107, the logic unit could recognizethis as being a correct state (i.e. amplifier 106 at logic 1 andamplifier 107 at logic 0) and produce a false output.

A delay circuit is therefore incorporated in the logic unit 127 toinhibit the output for approximately 40p. sec after detection byamplifier 106, by which time amplifier 107 will have produced adetection signal.

A circuit diagram of the amplifier 106 is shown in FIG. 5, the amplifier107 being similar. Transistors TRl and TR2, with their associatedresistors, form a conventional AC pulse amplifier driving an outputtransistor TR3. During steady state conditions (i.e. no billet beingdetected) the transistors TRl and TR2 are conducting slightly, and thetransistor TR3 is biased to saturation by resistor R1. The amplifieroutput from the collector of the transistor TR3 is at logic 0.

When the photo-diode 118 detects a billet, its resistance falls, andforward biases the transistor TRl causing it to conduct heavily. Thecharge on the emitter of the transistor TRl is AC coupled to the base ofthe transistor TR2, forward biasing the latter and causing it tosaturate. The fall on the collector of the transistor TR2 reverse biasesthe transistor TR3, cutting it off, and the amplifier output on anoutput conductor 128 switches rapidly to a positive voltage.

The photo-diode 118 detects the billet intermittently, due to therotation of the mirror 108, and thus generates a series of pulses in theamplifier 106. A variable resistor RVl controls the width of the pulsefrom the amplifier 106 by controlling the gain, and hence the period ofsaturation, of the transistor TR2.

Conductor 131 is referenced to a positive voltage by zener diode D], aresistor R2 and the positive supply voltage on conductor 129. CapacitorC1, C2 and C3 decouple conductors 129, 130 and 131 and a diode D2 on thebase of the transistor TR3 limits the negative voltage of the base.

The chopper amplifier 126 is shown in more detail in FIG. 6 andcomprises an operational amplifier or comparator 132 connected in acomparator mode, driving an output stage transistor TR4.

When infra-red radiation from the cell 123 is detected by thephoto-diode 124, the diode resistance is reduced, and the potential atthe cathode of the diode 124 falls until it is more negative withrespect to the comparitor reference potential at the junction ofresistors R3 and R4. At this point, the comparator 132 switches over,and its output changes rapidly from negative voltage to a positivevoltage, driving transistor TR4 into saturation. The output from thecollector of the transistor TR4 switches from a positive voltage tozero.

When one of the vanes of the disc 122 cuts off the radiation to thephoto-diode 124, the diode resistance increases and the voltage at thecathode increases until it is more positive than the referencepotential. The comparator 132 then switches back, cutting off thetransistor TR4, and the output on an output conductor 133 rises.

Diode D3 prevents the base of the transistor TR4 from going too farnegative. A resistor R7 limits the current from the comparator 132.Capacitors C4, C and resistor R5 provide frequency compensation for thecomparator. Capacitors C6 and C7 decouple the conductors 134 and 135.

The cell 123 is connected in series with a resistor R6 between 0 voltand negative terminals.

The logic unit 127, shown in FIG. 7, comprises commercially availableMEL series 10 circuit blocks.

The signal from amplifier 106 on conductor 128 is shaped and inverted bya pulse shaper and inverter B, inverted by an inverter C, and applied toa gate D.

The inhibit signal from the chopper amplifier 126 on conductor 133 isapplied directly to the gate D.

When all the inputs on the gate D are at logic l the output on conductor136 falls to logic 0, i.e. the gate performs a nand function. This statewill only occur when amplifier 106 is at logic l amplifier 107 at logic0', and the chopper amplifier inhibit signal at logic l The output onconductor 136 is connected to the second half of the gate D, and theinverted output on conductor 137 is applied to a pulse shaper E, viaresistor R8. A network comprising resistors R8, R9 and R10 and capacitorC8 delays the application of the signal to pulse shaper E for 40p. sec,to prevent a false detection in the event the leading edge of the signalfrom the amplifier 107 lagging the leading edge of the signal from theamplifier 106.

The output of the pulse shaper E goes to logic 0 and triggers a pulsedriver F. The output of pulse driver F is a pulse of p. secs durationfrom logic l to logic 0 on an output conductor 138.

I claim:

1. In apparatus for detecting an object comprising means for scanningtwo adjacent parallel paths, and radiation responsive means associatedwith said scanning means for sensing radiation from said two parallelpaths and indicating said object defined thereby, said radiationresponsive means comprising means for producing, in response tovariations in the radiation along each of said paths, signalsrespectively associated with said paths, and means responsive to saidsignals for indicating the presence or absence of the object in each ofsaid paths, aperture means positioned between said radiation responsivemeans and said scanning means, said aperture means having edge portionsdefining limits for the lengths of the scans of said two parallel pathssensed by said radiation responsive means, the improvement comprisingmeans for inhibiting said radiation responsive means at and adjacent thelimits of the scans of said paths defined by the edge portions of saidaperture means.

2. The apparatus of claim 1, wherein said scanning means comprise amovable mirror and drive means for moving the movable mirror to scansaid paths, and said inhibiting means comprise a radiation source, aradiation detector connected to receive radiation from said radiationsource, a shutter mounted for movement by said drive means between saidradiation source and said radiation detector in synchronism with themovement of said mirror to blank said radiation detector at the limitsof the scans defined by said edge portions, and said radiation detectorconnected to said radiation responsive means to generate signal means inresponse to the blanking by said shutter to inhibit said radiationresponsive means.

3. The apparatus of claim 2, wherein said mirror and said shutter aremounted for rotation by said drive means, said mirror being multi-sidedand said shutter having vanes corresponding to the sides of said mirror.

1. In apparatus for detecting an object comprising means for scanning two adjacent parallel paths, and radiation responsive means associated with said scanning means for sensing radiation from said two parallel paths and indicating said object defined thereby, said radiation responsive means comprising means for producing, in response to variations in the radiation along each of said paths, signals respectively associated with said paths, and means responsive to said signals for indicating the presence or absence of the object in each of said paths, aperture means positioned between said radiation responsive means and said scanning means, said aperture means having edge portions defining limits for the lengths of the scans of said two parallel paths sensed by said radiation responsive means, the improvement comprising means for inhibiting said radiation responsive means at and adjacent the limits of the scans of said paths defined by the edge portions of said aperture means.
 2. The apparatus of claim 1, wherein said scanning means comprise a movable mirror and drive means for moving the movable mirror to scan saId paths, and said inhibiting means comprise a radiation source, a radiation detector connected to receive radiation from said radiation source, a shutter mounted for movement by said drive means between said radiation source and said radiation detector in synchronism with the movement of said mirror to blank said radiation detector at the limits of the scans defined by said edge portions, and said radiation detector connected to said radiation responsive means to generate signal means in response to the blanking by said shutter to inhibit said radiation responsive means.
 3. The apparatus of claim 2, wherein said mirror and said shutter are mounted for rotation by said drive means, said mirror being multi-sided and said shutter having vanes corresponding to the sides of said mirror. 